Pump damping means



Jan. 14, 1964 T. BUDZICH 3,117,524

PUMP DAMPING MEANS Filed Oct. 20, 1959 4 Sheets-Sheet 1 INVENTOR. TADEUSZ BUDZ/CH BY RIC/1'5), Ms NENN r4 FA ER/NG TON Jan. 14, 1964 T. BUDZICH 3,117,524

PUMP DAMPING MEANS Filed Oct, 20, 1959 4 Sheets-Sheet 2 INVENTOR. TADEUSZ BUDZ/CH BY [ff/CHE Y, MENE/VN Y& FA BRING TON JmJ/U' mxs Jan. 14, 1964 1-. BUDZICH PUMP DAMPING MEANS 4 Sheets-Sheet 3 Filed Oct. 20, 1959 BY ICHEXMSA/ENNYJEFAER/NGTON M 0 7 74i AT F/VE'YS Jan. 14, 1964 T. BUDZICH 3,117,524

PUMP DAMPING MEANS Filed on. 20, 1959 4 Sheets-Sheet 4 l N IN VEN TOR. f 73405052 BUDZ/CH M 3 TTgP/VEYS Weatherhead Company, Cleveland, Ohio, a corporation of Ohio Filed Oct. 20, 1959, Ser. No. 847,512 7 Claims. (Cl. 103-37) This invention relates to pumps and more particularly to constant pressure, variable volume output pumps of the type disclosed in my co-pending application Serial No. 825,005, filed July 6, 1959, now Patent No. 3,087,432, of which the instant application is a continuation-in-part.

The pump of my said co-pending application comprises a pump housing and a cylinder block which is mounted for axial movement within the housing. The cylinder block is provided with a plurality of pistons which are progressively reciprocated in the cylinder block by an inclined drive mechanism within the pump housing. The cylinders are each provided with a reaction piston leading to an outlet check valve whereby the output of all of the pistons is directed to an outlet chamber at one end of the pump housing.

The pump drive mechanism of my said co-pending application is also disclosed and claimed in co-pending continuation-impart application, Serial No. 17,832, filed March 28, 1960. The instant application is directed more particularly to the means provided for varying the displacement of the pumping cylinders.

It is among the objects of my invention to provide a pump having a cylinder block wherein the cylinder block is provided with a plurality of cylinders and wherein pistons are arranged to be reciprocated in the cylinders and wherein the cylinder block is moved so as to vary the volume output of each cylinder in response to a predetermined change in pressure at the outlet of the pump.

It is a further object of my invention to provide a pump according to the preceding object wherein the cylinder block is mounted for sliding movement on a guide within the pump housing and wherein the guide and cylinder block are constructed and arranged soas to form cooperating parts of means responsive to outlet pressure changes to move the cylinder block along the guide and thereby vary the pump displacement.

it is a further object of my invention to provide a pump according to the preceding object wherein a pump housing is provided with an end plate having a hollow guide portion thereon projecting within the pump housing and wherein the pump housing is provided with an end cap having an outlet chamber and wherein said end plate is provided with a bore concentric with said hollow guide portion on the end plate and a reciprocating valve member is carried within said hollow guide which reciprocating valve member is subjected to outlet pressure and whereby the valve member may be moved to admit fluid from the outlet chamber into the hollow guide and thence to a fluid piston and cylinder efi'ective to move the cylinder block and change the displacement of the pump.

It is a further object of my invention to provide a pump according to the preceding objects wherein the movement of the cylinder block between maximum and minimum displacement positions is dampened and one wherein the effectiveness of the dampening is increased progressively as the cylinder block moves toward its minimum displacement position.

It is a further object of my invention to provide a pump according to the preceding objects wherein the dampening of the cylinder block movements varies inversely with the volume output to provide maximum dampening at the lower output ranges of the pump.

It is a further object of my invention to provide a pump having unloading means effective to open a passage- 3,ll?,52i Patented Jan. 1%, 1%64 way between the pump outlet and the hydraulic fluid at the inlet side of the pump as the pump is started in operation and wherein said passageway is held open during the first few revolutions of the pump operation.

It is a further object of my invention to provide an unloading means whereby the pump is characterized by low torque requirements at the start of its operation.

Further objects and advantages relating to efiiciency in operation, ruggedness of construction, ease of assembly and low cost manufacture will appear from the following description and the appended drawings wherein:

FIG. 1 is a sectional view of a pump made according to my invention;

FIG. 2 is an enlarged sectional view of the control valve employed in the pump made according to my invention;

FIG. 3 is a sectional view similar to FIG. 1 showing the valve member moved to a position effective to increase the volume displacement of each of the cylinders in the P p;

PEG. 4 is a sectional view of a modified form of pump showing the pistons in maximum displacement position;

FIG. 5 is a view similar to FIG. 4 showing the pistons in minimum displacement position;

FIG. 6 is a sectional elevation with parts broken away to illustrate the dampening means forming a part of a pump according to my invention;

FIG. 7 is a sectional elevation showing the pump unloading means and a modified form of dampening device for a pump according to my invention; and

FIG. 8 is an enlarged sectional view of the unloading valve forming a part of the pump unloading means.

Referring to the drawings, the pump made according to my invention comprises a cup-shaped housing 6 having an opening in one end as at 7 to receive a driving shaft 3. The driving shaft 8 may be equipped with a pulley or chain sprocket and is adapted to be driven by a power unit such, for example, as an automobile engine. The housing 6 is preferably provided with a radially extending mounting flange 9 apertured as at 10 for receiving the mounting bolts.

The left-hand end of the housing 6 is provided with an end cap 12 bolted to the housing as at 13. A guide assembly indicated in its entirety as at 15 includes a plate 16 clamped between the end cap 12 and the body of the housing 6. integrally formed with the plate 16 is a tubular guide member 17 projecting centrally of the interior of the housing 6. Dowel pins, such as 18, are received within complementary bores in the end cap 12 and the plate 16 to facilitate the assembly of the guide member 15 within the housing.

The cylinder block indicated in its entirety as at 29 is provided with a plurality of angularly spaced cylinder bores 21. A groove 22 is machined in the cylinder block to a depth sufficient to cut through the walls of the cylinders 21 to provide an inlet port 23 in each of the cylinders. Each cylinder is provided with a piston 25 and each piston is reciprocated in the cylinder by a piston rod 26 driven by the rocking driver member 27.

The end of the tubular guide 17 receives a boss 29 which is integrally formed with a plate 30 and the plate 39 is apertured in alignment with each of the pistons 25. A spring 31 surrounds each of the pistons 25 and one end of the spring 31 abuts against a flange 32 at the end of the piston. The other end of the spring 31 abuts against the plate 30 in the recess 33 surrounding the piston 25. When the piston 25 is advanced into the cylinder 21 by means of the piston rod 26 and the driver 2'7, fluid forward of the piston 25 is advanced through the reaction piston 36 to the check valve 37 and thence through passageway 38 to the outlet chamber 39.

The end 8a of the driver shaft 8 is journaled in a central aperture in the plate 3%) and the opening around the shaft 8 is provided with a seal 46. The interior or" the cylinder block is provided with a counterbore as at 41 and this counterbore snugly fits around a reaction member d2 which is secured near the end of the tubular guide 1? at its exterior. The space between the reaction member 42 and the leithand end of the counterbore 41 is indicated at 44. The member 42 is in the form of a ring scaled to the exterior of the guide 17 where it is retained in place by a snap ring in a groove in the guide. This space id provides a reaction chamber 44 and fluid under pressure is admitted into the reaction chamber 44 by way of the aperture 45 through the wall of the tubular guide 1'7.

The cylinder block 29 is normally biased to the righthand as viewed in FIG. 1 so as to reach the limit of its travel as provided by the pin 47 and the slot 48. The bias to the right is provided by the plurality of springs 4'9 interposed between the left-hand end of the piston block 2.9 and the end of the reaction piston 36. Thus the cylindcr block 2% is biased by the springs 49 to a position of maximum displacement. When fluid under pressure is admitted to the reaction chamber 44, the piston block 243 is moved to the left so as to move the piston block to a position of lesser displacement.

The control means for determining the position of the cylinder block 26 is provided by a plunger assembly indicated in its entirety as at The interior of the guide 17 forms a chamber 51 which is in communication with the port 35 leading to the reaction chamber 44. One end of this chamber 51 is closed by a plug 52 and the other end of the chamber is provided with an axial bore having disposed therein the plunger 53 of the control valve. That end of the control valve plunger 53 disposed within the chamber 5i is provided with a cap 54. One end of the cap is recessed to receive a ball 55 which ball is retained by spring retainer 56 arranged to receive one end of the spring 57 disposed in the chamber Sl.

The plunger 53 is provided with a central bore having therein a rod 58. One end of the rod 58 bears against the inside of the cap 54 and the other end of the rod 58 bears against an adjusting screw 59. By turning the screw 59 inwardly along the threads provided therefor in the plunger body 53, the rod 58 may be moved so as to adjust the cap 54 axially of the plunger body. This arrangement provides for adjusting the overall length of the plunger body 53 and the loading on the spring 57 which biases the plunger body 53 towards the outlet.

The outlet chamber 39 is provided with a bore 6% which receives the plunger boss 61 fitted therein and sealed in position in the bore all by means of O-ring seal 52. In FIG. 2 the control body 53 is positioned so that fluid pressure from the outlet chamber 39 may flow through the passageway 63, thence through the annular chamber 64- on the plunger body and thence outwardly through passageway 55 and passageway 66 into the chamber 51. Fluid thus admitted to the chamber 51 moves by way of the port 45 into the reaction chamber and is efiective to move the cylinder block Ztl to the left, thus reducing the displacement of each of the cylinders 21.

Two extreme positions of the control plunger 53 are shown in FIGS. 2 and 3, respectively. The position of FIG. 2 illustrates the plunger 53 as moved to a position where hydraulic iluid from the outlet is admitted to the chamber 51 and thence into the chamber 44 to move 16 cylinder block. FIG. 3 illustrates the position of the plunger wherein fluid from the chamber 44 and the chamber 51 is being discharged into the low pressure side of the pump. When the forces acting on the control plunger 53 are in balance, the plunger is in a position corresponding to that illustrated in FIG. 1 wherein fluid is neither being added to the chamber 51 from the outlet port nor being discharged from the chamber 51 into the low pressure side of the pump. The pump may be designed to have a constant output pressure of, for example, about 2000 pounds and accordingly the balanced condition of the control plunger 53 may be obtained at any position of the cylinder block between maximum displacement and minimum displacement.

The outlet pressure is acting against the cross-sectional area of the end of the plunger 53 tending to push the plunger to the right as viewed in FIG. 2 so that fluid may move from the outlet chamber along the reduced diameter portion 54, at the exterior of the plunger and thence through a port 65 and into the chamber 51. At the end of the plunger 53 within the chamber 51 the spring 57 is acting so as to oppose the outlet pressure on the plunger 53. The hydraulic fiuid pressure in the chamber 53 supplements the action of the spring 57 tending ot move the control plunger 53 to the left as viewed in FIG. 2. The hydraulic fluid pressure in the chamber 51, however, is a function of the springs 49 surrounding the reaction piston 36. The series of springs 49 tend to bias the cylinder block 20 to its maximum displacement position and thus apply a pressure to the hydraulic fluid in the chamber 44. Heavy springs 49 would apply a correspondingly heavier fluid pressure in chamber 44 than if light springs were used at 49.

Accordingly it will be understood that relatively small changes in fluid pressure occur within the chamber 51 and that the fluid pressures in chamber 51 are but a small fraction of the fluid pressure in the outlet chamber 39. For example, the fluid pressures in the chamber 51 may drop to inlet pressure when the plunger is in a position as shown in FIG. 3 and fluid pressure is being discharged from the chamber 51. The spring 57, however, continues to bias the plunger 53 to the left. Go the other hand, when fluid is being introduced to the chamber 51, as illustrated in FIG. 2, the fluid pressure may reach about 200 pounds in the chamber 51. It will be understood that as the cylinder block is moved from its position of maximum displacement toward a position of minimum displacement, the springs 4-9 are being compressed. Accordingly, a higher pressure is obtained within the chamber 51 at low volume displacement than would exist when the cylinder block is at its position of maximum displacement.

The cylinder block position control means results in a sensitive arrangement wherein the position of the cylinder block is accurately controlled by fluid pressures about one-tenth of the fluid pressure at the pump outlet. Such lower pressures employed for controlling the cylinder block position result in lower leakage characteristics in the control system and permit the use of a relatively simple valving system for handling such lower pressures.

During the operation of the pump, fluid is introduced to the interior of the pump housing 6 by way of the inlet 6a and is discharged from the housing at the outlet 61;. Accordingly the interior of the pump housing is filled with fluid at low pressure throughout the pump operation.

In the modified form of pump illustrated in F188. 4 and 5, the pump housing 89 is provided with an end cap 83 and a plate 32 is clamped in position between the pump housing 30 and the end cap 33. The plate 82 is provided with a pair of concentric bosses 31 and 88. The outermost boss 81 is provided with a smooth cylindrical surface 81:: which serves to guide the cylinder block 116 for axial movement. The innermost boss 88 receives a control assembly indicated as at 8'7 and the outer surface of 37 is a smooth cylindrical surface arranged to guide a piston member 113.

The member 113 includes a tubular section 116 riding on the smooth cylindrical exterior of the control member 87. In this form of pump the cylinder block lit) is substantially annular in cross-section with the inner periphery riding on the surface 816: and the outer periphery having inlet ports 122 out thereinto so as to permit hydraulic iiuid to enter the cylinders 121. The inner cylindrical suriace a of the cylinder block lllll is provided with a counterbore T15 to receive a flange 114 at the periphery of the piston member 113. The member 81 which supports the cylinder block is provided with an aperture 81b. When the piston 113 is moved to the left, as shown in FIG. 4, the fluid enclosed by the boss 81, the piston 113 and the inner wall 110:: of the cylinder block 110 must escape from this space since the space is being reduced in volume. Part of the fluid escapes through the port 81b. It will be observed from FIG. that the leading edge 11% of the cylinder block 110 reduces the open area of the port 81b so that as the cylinder block approaches its minimum displacement position the dampening effect of the fluid port 8111 is increased.

As in the embodiment previously described, each pumping cylinder 121 is provided with a reaction piston 119 having an outer free end arranged to bear against the end 84.: of the tubular portion of a check valve 84. Springs 118 are arranged around each of the reaction pistons 119 and one end of the spring 118 bears against the cylinder block 110 and the other end of the spring 118 bears against the flange on a sleeve 118a mounted on the outer end of the reaction piston 119. At least one of the reaction piston sleeves is proportioned axially to enter the recess in the end plate around the check valve to prevent rotation of the cylinder block.

The interior of the pump housing is provided with a counterbore 101 at its outlet end terminating in a shoulder 102 which serves as an abutment for a flange 103 at the periphery of a supporting disc 104. The member 104 is provided with a boss 105 centrally thereof which receives a bushing 106 for the inner end 107 of the drive shaft 108. The member 104 is apertured as at 104a to permit the fluid flow from the interior of the pump to and fro through the opening 810 of the piston 113 during the dampening action. The member 104 is also apertured to receive the ends of the pistons 123 which are reciprocated by an angular drive arrangement as in the preferred embodiment.

The supporting member 104 is inserted Within the pump housing from the open outlet end thereof during the assembly of the pump and when the flange 103 thereof is against the shoulder 102 in the housing, a sleeve 101a is arranged at the interior of the pump in counterbore 101 and is held in position by hearing against the end plate 82.

A sleeve or reaction member 130 is mounted on the inner end of the member 87 and one end of the sleeve, as at 131, bears against the radial face of the member 104. The annular portion 132 of the sleeve 130 is provided with a seal fitting the exterior of the cylindrical surface of the member 87 and said enlargement 132 forms with the interior of the piston member 113 a chamber 94 adapted to receive hydraulic fluid coming thereinto by way of the port 133 in the wall of the member 87. The control means of this form of my invention is constructed and arranged to operate substantially as in the preceding embodiment in that as the outret pressure increases beyond a predetermined maximum, fluid is introduced into the chamber 94 and the piston 113 is effective to move the cylinder block 110 to a position of lesser displacement, as illustrated in FIG. 5. Moving the cylinder block 110 under the action of the control from right to left displaces hydraulic fluid outwardly through the ports 81b and 81c. The higher the pressure difference necessary to effect flow through the ports 81b and 81c, the higher the dampening action of the ports. This construction, in effect, provides a dash-pot and its dampening action is proportional to the square of the velocity of the cylinder block 110 in its movements.

The dampening of the cylinder block movement may also be accomplished by the apparatus illustrated in FIGS. 6 and 7. In the form of my invention illustrated in PEG. 6 a pump housing 200 is provided with an end cap 201 having an outlet 203 and a cylinder block 204 mounted for axial sliding movement along the cylindrical exterior of the guide member 205. The cylinder block 6 204 is provided with a plurality of cylinders as indicated at 206. Each of the cylinders 206 is provided with a reaction piston 207 arranged to conduct hydraulic fluid under pressure to the check valve indicated in its entirety as at 208.

The end of the housing 200 adjacent the end cap 201 is provided with a counterbore 209 and a shoulder 210. The annular sleeve 211 has a large diameter portion 212 with an axial extent corresponding to the length of the counterbore 20? so that when the member 211 is assembled within the pump housing it is retained in position by its interior cylindrical surface 213 snugly surrounding the boss 214 formed integrally with the end plate 215.

The shoulder 210 of the housing prevents displacement axially of the annular member 211. The member 211 functions somewhat as a cylinder and its inner cylindrical surface, indicated at 216, slidably receives the cylindrical surface 217 at the exterior of the cylinder block 204.

The annular cylinder member 211 is provided with a series of apertures indicated at 220, 221 and 223. It will be understood from the preceding description of my pump that when the pump is at maximum displacement the space between the radial face 20461 of the cylinder block 204 and the end plate 215 is filled with hydraulic fluid at pump inlet pressure. When the cylinder block 204 moves to a position of minimum displacement a part of the hydraulic fluid in the chamber 225 must be forced out of the space into the low pressure space 226 surrounding the cylinder block. Preferably the apertures 220-223 in the annular member 211 increase in diameter so that aperture 220 is the smallest, 221 slightly larger and 223 is the largest of the three illustrated in the series.

As the cylinder block 204 moves toward a position of minimum displacement the leading edge defined by the face 204a progressively reduces the area of escape for the fluid in the chamber 225. The cylindrical section 217 of the cylinder block functions as a piston moving in the dampening cylinder 211. The control plunger 227 operates within the guide member as described in connection with the earlier embodiments and the cylinder block is moved to and fro along the member 205 to vary the displacement volume. Depending upon the velocity of the cylinder block 204, the rate of oil discharged through the apertures 220221-223 will vary. The higher the velocity of the piston, the higher the rate of the flow of oil and, therefore, the higher the pressure drop along the apertures. Since the pressure drop generated by the apertures such as 220, 221 and 223 is proportional with the square of the velocity of the cylinder block 204, the dampening will be much more effective at the higher speeds and will influence the control very little at low speeds of the cylinder block 204.

It will be understood that in this form of the invention, as in the forms earlier described, reaction springs are interposed between the end plate 215 and the cylinder block 264 and that a difference exists between the available force for control between the extended maximum stroke position and the minimum stroke position. The available forces for actuation of the cylinder block 204; in the region of small volume outputs are higher than those in the full extended position of the cylinder block 204.

A modified form of dampening cylinder and piston arrangement is illustrated in the pump shown in FIG. 7 wherein a pump housing 300 is provided with an end cap 301 and a plate 302 which is clamped between the housing 300 and the end cap 301. The plate 302 is formed to provide an axially extending cylindrical boss 303 which serves to support and guide the piston block 304. In the piston block illustrated, the forward end of the piston block is not circular, but is grooved axially as at 304a and could not function as a piston within a dampening cylinder. Accordingly an adaptor piston 305 is mounted on the end of the cylinder block 304 and the 7' adaptor 395 has a cylindrical outer surface which fits within the dampening cylinder 306.

The cylinder 3% is constructed and arranged substantially as in the embodiment of FIG. 6 in that it is clamped between the end plate 382 and the housing 3%. The dampening cylinder 3% is provided with apertures such as 397 and 388 which are constructed and arranged substantially as in the preceding embodiment and perform the same functions with respect to the dampening of the cylinder block movements as the cylinder block moves to different displacement positions.

In the form of pump illustrated in FIG. 7 a pump unloading mechanism is provided. It will be appreciated by those skiiled in the art that where the pump may remain stationary for a long period of time, the bearing assembly for driving the pistons is continuously subjected to an axial force by the piston return springs, such as springs 31 of FIG. 1. This spring force supplied over a period of time will tend to squeeze the oil from the mating bearin" surfaces and thus there is created the possibility that on stopping and starting at full load a metal-to-metal contact may take place in the bearings. In certain installations of the pump as, for example, where the pump is to be driven by an electric motor, it is desirable to reduce the pump starting torque for the starting windings of the motor and thus permit the use of a smaller electric motor than that required to overcome the pump starting torque without the unloader.

The end cap 392 is provided with an outlet 310 leading to line 311, check valve 312 and to use line 313. The check valve 312 prevents the application of fluid pressure from accumulators or other accessories in the use line 313 from coming back into the pump. The check valve is arranged to permit free flow in the direction from line 311 to line 313. The outlet 310 communicates with a bore 314 which leads to the check valve chamber 315. The chamber 315 in turn opens into a bore 316 leading to unloading valve chamber 317. The unloading valve is indicated in its entirety in FIGS. 7 and 8 as at 318.

The plate 392 is provided with an axial passageway 319 which terminates in a valve seat 320. The unloading valve, as shown in the enlarged view of FIG. 8, includes .a valve closure portion 321 which fits in the seat 320 to close the passageway 319 during the normal operation of the pump. The unloading valve 318 includes a central chamber 322 and an outer fimge portion 323 which forms a chamber for a spring 324 normally biasing the valve 313 in an open position. During the normal operation of the pump the outlet pressure at 316 will be effective against the unloading valve 318 and thus tend to hold the portion 321 in the valve seat 320.

The wall of the chamber 322 in the unloading valve is provided with apertures 325 opening into the chamber which encloses the spring 324 and thus when the unloading valve is moved to an open position in response to spring 324, fluid flow from the outlet 310 may enter the passageway 319 and thence back into the low pressure area of the pump housing.

Upon stopping the pump, the pump control plunger 328 is inactive and therefore the pump is at its position of maximum displacement. It will be understood that the cylinder block remains in its maximum displacement position until the control level of the discharge pressure in 31% is reached.

With the unloading valve 313 open, as above described, the passage between the outlet 310 and the pump and the inlet of the pump is open and thus prevents the build-up of high discharge pressure. The check valve 312 isolates the pump from the hydraulic circuit which may be under pressure particularly in the event accumulators are used in the use line 313. With the outlet of the pump directly connected to the inlet side of the pump by way of passage 319, no pressure is generated during the first few revolutions of the pump drive mechanism. Since the pump is at its maximum displacement stroke with the starting loads being small,- thepump mechanism will be gradually accelerated increasing the flow output of the pump. This continuously increasing volume of flow must be moved from the. pump outlet 310 through passage 314, thence through the check valve chamber 315, thence through passage 316, thence through the openings 325 in the unloading valve and thence around the end portion 321 of the unloading valve and into passageway 319 of the pump.

Gradually increasing volume flow of oil will produce proportional pressure differential at the points of maximum resistance which occurs at the valve seat 329. The force induced by this pressure diiierence opposes the spring 324 and finally closes the passageway 319 by moving the unloading valve into closed position as shown in FIG. 8. When this occurs the flow is from the output to line 311, thence through check valve 321 to the use line 3E3. When the pump begins to stop, the gradually decreasing revolutions per minute of the drive will drop to a level at which the pump is no longer capable of sustaining leakage inherent in the moving parts of the pump. Under the influence of back flow the check valve 312 will close and the pump will come to a gradualstop being progressively unloaded by its own leakage.

Although I have disclosed and described different forms of my invention, it will be understood that numerous colorable variations may be made therein without departing from the scope of theinvention as defined in the following claims.

lVhat is claimed is:

1. A pump comprising an elongated hollow housing having an inlet and an outlet, an axial guide member mounted at one end of said housing and extending therein, a cylinder block mounted for axial sliding movement along said guide member, said cylinder block having a plurality of piston bores therein, a piston mounted for reciprocation in each of said bores, means at the other end of said housing to reciprocate said pistons, a reaction piston in each of said cylinders, 21 check valve mounted in the housing in alignment with each of said reaction pistons and passageways to conduct hydraulic fluid under pressure from said check valves to said outlet, means to present rotational movement of the cylinder block, control means for moving said cylinder block to vary the output displacement, said control means comprising spring means around each of said reaction pistons biasing the cylinder block along said guide to its maximum displacement position, hydraulic cylinder and piston means operatively arranged between said cylinder block and said guide, said hydraulic cylinder and piston means having a substantially smaller cross-sectional area than said cylinder block, a control plunger movable to one position effective to introduce fluid pressure from said outlet to said hydraulic cylinder and movable to another position to discharge fluid from said hydraulic cylinder into said pump housing, one end of said plunger being subject to hydraulic pressure at said outlet, the other end of said plunger having spring means biasing the plunger in opposition to said outlet pressure, said other end of said plunger being also subjected to the hydraulic pressure effective in said cylinder whereby said cylinder block may be moved toward its position of minimum displacement by hydraulic fluid pressures which are substantially less than the hydraulic pressures effective at said outlet, and dampening means including a cylinder carried by the housing and a piston associated with the block to dampen cylinder block movement.

2. A pump comprising a housing having an inlet and an outlet, a guide member in said housing, a cylinder block mounted for limited axial movement along said guide member from a position of maximum displacement to a position of minimum displacement, said cylinder block having axial cylinder bores therein, pistons in said cylinder bores, drive means to reciprocate said pistons, spring means normally biasing said cylinder block to a position of maximum displacement, hydraulic means responsive to pressure changes in the outlet effective to move said cylinder block to a position of minimum displacement, and hydraulic dampening means to dampen the motion of the cylinder block, said dampening means including variable orifice means decreasing in area as said cylinder block moves toward the minimum displacement position, said dampening means increasing in effectiveness as the cylinder block approaches its minimum displacement position.

3. A pump comprising a housing having an inlet and an outlet, a guide member in said housing, a cylinder block mounted for limited axial movement along said guide member from a position of maximum displacement to a position of minimum displacement, said cylinder block having axial cylinder bores therein, pistons in said cylinder bores, drive means to reciprocate said pistons, spring means normally biasing said cylinder block to a position of maximum displacement, hydraulic means responsive to pressure changes in the outlet effective to move said cylinder block to a position of minimum displacement, and hydraulic dampening means to dampen the motion of the cylinder block, said dampening means comprising a cylinder for fluid, a piston portion on the cylinder block and ports in the cylinder varying the restriction to fluid flow during the piston block travel.

4. A pump comp-rising a housing having an inlet and an outlet, a guide member in said housing, a cylinder block mounted for limited axial movement along said guide member from a position of maximum displacement to a position of minimum displacement, said cylinder block having axial cylinder bores therein, pistons in said cylinder bores, drive means to reciprocate said pistons, a dampening cylinder on the housing to receive said cylinder block, spring means normally biasing said cylinder block to a position of maximum displacement, hydraulic means responsive to pressure changes in the outlet effective to move said cylinder block to a position of minimum displacement, said dampening cylinder having ports therein adapted to be closed by the cylinder block as the cylinder block approaches its minimum displacent position.

5. A pump comprising a housing having an inlet and an outlet, a guide member fixed wimin the housing, a cylinder block mounted for movement on said guide member to positions of maximum and minimum displace ment, said cylinder block having axial cylinder bores therein, pistons in said cylinder bores, drive means to reciprocate said pistons, means to dampen the motion of the cylinder block along said guide member comprising a dampening cylinder concentric with said guide member, a dampening piston movable Within said cylinder carried by said cylinder block, said dampening cylinder having an apertured wall whereby hydraulic fluid Within the cylinder is discharged through said Wall apertures as the piston and cylinder block move toward a position of minimum displacement.

6. A pump com-prising a housing having an inlet and an outlet, a cylinder block mounted for axial movement Within said housing from a position of maximum displacement to minimum displacement, said cylinder block having axial cylinder bores therein, pistons in said cylinder bores, drive means to reciprocate said pistons, means to dampen the movements of said cylinder block comprising a dash-pot cylinder member surrounding said cylinder block and forming therewith a dash-pot chamber to receive hydraulic fluid, said dash-pot chamber having a series of axially displaced openings therein characterized in that the opening adjacent the minimum displacement position of the cylinder block movement is smaller than the opening at the maximum displacement position of the cylinder block movement whereby the dampening effectiveness is increased as the cylinder block approaches its position of minimum displacement.

7. A pump comprising an elongated cup-shaped housing, an end plate adapted to close the open end of said cup-shaped housing and an end cap covering said end plate and attached to said housing, said end plate having a guide member extending longitudinally Within the housing, a cylinder block mounted on said guide member for limited movement from a position of maximum displacement to a position of minimum displacement adjacent said end plate, said cylinder block having axial cylinder bores therein, pistons in said cylinder bores, drive means to reciprocate said pistons, spring means biasing the cylinder block to maximum displacement position, hydraulic means to move the cylinder block to its position of minimum displacement, a dampening cylinder mounted on said end plate and extending axially therefrom towards said cylinder block, means on said cylinder block adiacent the end plate circular in cross-section and proportioned to fit snugly Within the open end of said dampening cylinder, said dampening cylinder having a series of openings therein, said openings being of different size and the largest of said openings being spaced axially a greater distance from the end plate than the smallest of said openings whereby hydraulic fluid Within the dampening cylinder is forced outwardly through said openings as the cylinder block approaches the end plate and its position of minimum displacement and the leading edge of the cylinder block is eifective to progressively cut 01f the area in the openings of said dampening cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 2,483,705 Levetus et al Oct. 4, 1949 2,678,607 Huiferd et a1 May 18, 1954 2,804,827 Rydberg Sept. 3, 1957 2,990,781 Tuck et al July 4, 1961 2,997,956 Stewart Aug. 29, 1961 3,003,422 Bessiere Oct. 10', 1961 3,004,492 Norlin Oct. 17, 1961 FOREIGN PATENTS 402,603 Great Britain Dec. 7, 1933 411,190 Italy Dec. 18, 1945 1,202,109 France July 26, 1959 

2. A PUMP COMPRISING A HOUSING HAVING AN INLET AND AN OUTLET, A GUIDE MEMBER IN SAID HOUSING, A CYLINDER BLOCK MOUNTED FOR LIMITED AXIAL MOVEMENT ALONG SAID GUIDE MEMBER FROM A POSITION OF MAXIMUM DISPLACEMENT TO A POSITION OF MINIMUM DISPLACEMENT, SAID CYLINDER BLOCK HAVING AXIAL CYLINDER BORES THEREIN, PISTONS IN SAID CYLINDER BORES, DRIVE MEANS TO RECIPROCATE SAID PISTONS, SPRING MEANS NORMALLY BIASING SAID CYLINDER BLOCK TO A POSITION OF MAXIMUM DISPLACEMENT, HYDRAULIC MEANS RESPONSIVE TO PRESSURE CHANGES IN THE OUTLET EFFECTIVE TO MOVE SAID CYLINDER BLOCK TO A POSITION OF MINIMUM DISPLACEMENT, AND HYDRAULIC DAMPENING MEANS TO DAMPEN THE MOTION OF THE CYLINDER BLOCK, SAID DAMPENING MEANS INCLUDING VARIABLE ORIFICE MEANS DECREASING IN AREA AS SAID CYLINDER BLOCK MOVES TOWARD THE MINIMUM DISPLACEMENT POSITION, SAID DAMPENING MEANS INCREASING IN EFFECTIVENESS AS THE CYLINDER BLOCK APPROACHES ITS MINIMUM DISPLACEMENT POSITION. 